| Summary: | Differences in the sensitivity of marine species to ocean acidification will influence the structure of marine communities in the future. Reproduction is critical for individual and population success, yet is energetically expensive and could be adversely affected by rising CO₂ levels in the ocean. We investigated the effects of projected future CO₂ levels on reproductive output of two species of coral reef damselfish, Amphiprion percula and Acanthochromis polyacanthus. Adult breeding pairs were maintained at current-day control (446 mu atm), moderate (652 mu atm) or high CO₂ (912 mu atm) for a 9-month period that included the summer breeding season. The elevated CO₂ treatments were consistent with CO₂ levels projected by 2100 under moderate (RCP6) and high (RCP8) emission scenarios. Reproductive output increased in A. percula, with 45-75 % more egg clutches produced and a 47-56 % increase in the number of eggs per clutch in the two elevated CO₂ treatments. In contrast, reproductive output decreased at high CO₂ in Ac. polyacanthus, with approximately one-third as many clutches produced compared with controls. Egg survival was not affected by CO₂ for A. percula, but was greater in elevated CO₂ for Ac. polyacanthus. Hatching success was also greater for Ac. polyacanthus at elevated CO₂, but there was no effect of CO₂ treatments on offspring size. Despite the variation in reproductive output, body condition of adults did not differ between control and CO₂ treatments in either species. Our results demonstrate different effects of high CO₂ on fish reproduction, even among species within the same family. A greater understanding of the variation in effects of ocean acidification on reproductive performance is required to predict the consequences for future populations of marine organisms.
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